单选题 Very few people could understand the lecture the professor delivered because its subject was very ______.
A. obscure B. indefinite C. dubious D. intriguing

【正确答案】 A

【答案解析】[解析] 四个选项的意思分别是：obscure费解的，模糊不清的；indefinite无限期的，不明确的；dubious可疑的，不可靠的；intriguing令人感兴趣的，有迷惑力的。句意是，几乎没人能听瞳教授的讲座，因为这个课题太令人费解了。所以正确答案是A选项，如：The point of his speech is obscure．(他发言的要点模糊不清。)